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Anish Moorthy df4ec5aada KVM: selftests: Allow many vCPUs and reader threads per UFFD in demand paging test
At the moment, demand_paging_test does not support profiling/testing
multiple vCPU threads concurrently faulting on a single uffd because

    (a) "-u" (run test in userfaultfd mode) creates a uffd for each vCPU's
        region, so that each uffd services a single vCPU thread.
    (b) "-u -o" (userfaultfd mode + overlapped vCPU memory accesses)
        simply doesn't work: the test tries to register the same memory
        to multiple uffds, causing an error.

Add support for many vcpus per uffd by
    (1) Keeping "-u" behavior unchanged.
    (2) Making "-u -a" create a single uffd for all of guest memory.
    (3) Making "-u -o" implicitly pass "-a", solving the problem in (b).
In cases (2) and (3) all vCPU threads fault on a single uffd.

With potentially multiple vCPUs per UFFD, it makes sense to allow
configuring the number of reader threads per UFFD as well: add the "-r"
flag to do so.

Signed-off-by: Anish Moorthy <amoorthy@google.com>
Acked-by: James Houghton <jthoughton@google.com>
Link: https://lore.kernel.org/r/20240215235405.368539-12-amoorthy@google.com
[sean: fix kernel style violations, use calloc() for arrays]
Signed-off-by: Sean Christopherson <seanjc@google.com>
History 2024-04-09 14:28:53 -07:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.